The invention relates generally to a monolithic integrated circuit complementary metal-insulatorsemiconductor oscillator circuit having a temperature compensated current source.
One of the problems often associated with the use of integrated circuit metal-insulator-semiconductor oscillators and particularly those embodying metaloxide-semiconductor field effect transistors (MOSFETs) lies in the fact that such oscillators are often unstable, with their period of oscillation being variable as the ambient temperature to which they are exposed changes. Several attempts have been made by those skilled in the art to solve the problem of temperature induced oscillator instability. One such solution has been achieved by using external resistive and capacitive components, connected to the pins of an integrated circuit package. This solution is inconvenient for the user of the integrated circuit in that such external components occupy additional space on a printed circuit board which is almost always at a premium. In addition, the use of external components increases the cost of a particular electronic circuit to the ultimate user. Other workers in the art have attempted to use ring oscillators or Schmitt trigger oscillators to achieve temperature stable oscillation periods. These attempts have, for the most part, been unsuccessful. A solution was proposed in the IEEE Journal of Solid State Circuits, Vol. SC-18, October, 1983 at pages 525-532 in an article entitled: "CONTROL LOGIC AND CELL DESIGN FOR A 4K NVRAM". Although the disclosed NMOS circuit did have a temperature compensation means, unlike the previously mentioned ring oscillator and Schmitt oscillator, it embodied a depletion mode field effect transistor, which would require additional process steps for fabrication as part of a CMOS integrated circuit.
A temperature compensated CMOS oscillator would be particularly useful as a temperature independent clock to generate timing signals for use in memory circuits such as electrically erasable programmable read only memories (EEPROM) and in particular for generating signals required by such circuits for any ERASE or WRITE operations.
What is needed is a temperature stable CMOS oscillator having all of its components implemented on a single integrated circuit die, so that a user of such an integrated circuit would not have to perform any additional engineering for or add any additional components to such a circuit.